Preparation of benzene and toluene



Dec. 25, 1962 HQNEYCUTT 3,070,637

PREPARATION OF BENZENE AND TOLUENE Filed Aug. 5, 1959 Naphtha ,lg l3 Reforming Zone 2 H MOP-Rich Reci cle Recycle 7 Fraction (ISO-WOT) l4 Separator lowBoiling aturates Extraction Zone v 2| I74 Benzene-Toluene Distillation Extract zone l70'220F saturates INVENTOR.

EARL M- HONEYCUTT AT ORNEY rates atet nee 3,07%,637 PREPARATHQN F BENZENE AND TGLUENE Earl M. Honeycutt, West Chester, Pa, assignor to un lgil (fempany, Philadelphia, Pa, a corporation of New ersey Filed Aug. 3, 1959, Ser. No. 831,392 2 Claims. (til. 260-668) This invention relates to the preparation of benzene and toluene by reforming low boiling naphtha containing C and C naphthenes and more particularly is directed to a method for increasing the quantity of benzene produced by reforming a naphtha boiling in the range of l50220 F. in the presence of a platinum-containing reforming catalyst.

Commercial processes for the production of aromatics such as benzene and toluene by dehydrogenation of the naphthenes present in the low-boiling fractions of straightrun petroleum naphthas with concomitant isomerization and hydrocracking of the acyclic components of the feed to a higher octane gasoline fraction, are well known to the art. In such processes the feed stock is contacted with a catalyst in the presence of added hydrogen, at

temperatures of from about 875 F. to 975 F. and at a pressure of from about 200 p.s.i.g. to about 600 p.s.i.g. A preferred catalyst for this type of operation comprises platinum impregnated on an alumina base, and the catalyst advantageously may contain a minor amount (e.g., 0.1 to 6.0%) of combined halogen. Generally the platinum content of the catalyst is in the range of 0.1% to I about 1.0%. Such catalysts possess dehydrogenation, isomerization and hydrocracking activities, and these activities are so balanced in the manufacture of the catalyst as to insure a maximum of dehydrogenation and isomerization activity but not sufficient hydrocracking activity to crack such straight chain parafiins as are not isomerized to isoparatfins during the reaction. The aromatics produced in the hydroforming operation conventionally are extracted from the reformate by means of a suitable solvent such as diethylene glycol containing a minor amount of water.

Reactions involved in the production of benzene involve dehydrogenation of cyclohexane and isomerization of methylcyclopentane to cyclohexane followed by dehydrogenation. In the production of toluene the reactions are dehydrogenation of methylcyclohexane, isomerization of dimethylcyclopentane to methylcyclohexane followed by dehydrogenation, and dehydrogenation and dehydrocyclization of heptane. In commercial practice the conversion of cyclohexanes to aromatics by means of the platinum-containing reforming catalyst occurs nearly completely or in other words, the yield of aromatics from the cyclohexane components of the naphtha charge approaches 100%. Also the conversion of dimethylcyclopentane to toluene is high. However, the conversion of methylcyclopentane to benzene characteristically is relatively low. Hence, the yield of benzene in conventional commercial practice generally is substantially lower than otherwise would be obtained if all the methylcyclopentane were converted.

An object of the present invention is to obtain a substantial increase in the benzene yield resulting from reforming a low boiling straight run naphtha.

In one embodiment of the invention, a straight run naphtha boiling in the range of 150220,F. is subjected to hydroforming conditions, including a temperature in the range of 875-975 F. and a pressure in the range of 200-600 p.s.i.g., in the presence of a platinum-containing reforming catalyst. The resulting reformate is extracted to separate a benzene-toluene extract from a saturated hydrocarbon raffinate which contains unconverted methylcyclopentane. The raflinate is then distilled to separate a fraction enriched in methylcyclopentane. This methylcyclopentane-rich fraction is recycled to the reforming step by hydroforming in admixture with the virgin charge. In this manner conversion of the methylcyclopentane to benzene is maximized and a substantial increase in the benzene yield is achieved.

The invention can also be practiced in a modified manner by hydroforming the methylcyclopentane-rich fraction, obtained in the manner above described, in a separate reforming operation instead of in admixture with the virgin naphtha charge. In commercial practice this can be done conveniently by utilizing a blocked-out type of operation and alternately charging the virgin naphtha and the methylcyclopentane-rich fraction to the reformer.

' The reformate obtained from hydroforming the methylcyclopentane-rich fraction can be extracted either separately or in admixture With raflinate obtained from the hydroformed virgin naphtha to remove the benzene and the resulting raffinate can be distilled, either alone or in admixture with raitinate obtained from processing the virgin naphtha, to separate a fraction rich in unconverted methylcyclop-entane which can be reprocessed.

The invention is more specifically described in conjunction with the accompanying drawing which is a schematic fiowsheet illustrating one manner of practicing the invention. The charge to the process is a straight run naphtha fraction boiling in the range of ISO-220 E, which typically may have the following composition:

Percent Methylcyclopentane 6 Cyclohexane 7 Methylcyclohexane 12 Dimethylcyclopentane 11 Benzene 2 Toluene 4 laraffins 58 Referring to the drawing, the charge naphtha, which enters the system through line it), is admixed with recycle hydrogen from line 11 and the mixture is heated by means not shown to a suitable reforming temperature in the range of 875-975 F., more preferably 910960 F., and introduced to reformer 12. A recycle fraction obtained as hereinafter described is also fed to the reformer via line 13. The reformer contains a platinum type reforming catalyst which preferably contains a minor amount of combined halogen. Reforming zone 12 may comprise a series of reactors with heaters between the reactors for supplying heat absorbed due to the endothermic reactions involved, as is customary in conventional reforming operations. The reforming zone should be operated at a pressure in the range of 200600 p.s.i.g., the molar ratio of hydrogen to hydrocarbon fed thereto should be in the range 2:1 to 5:1 and the space rate in the reactors should be in the range of 1-5 volumes of hydrocarbon per volume of catalyst per hour. The products from the reforming step pass to condensing and separating means, indicated at 14, from which hydrogen is recycled through line 11 with excess hydrogen being withdrawn from the system via line 15.

The liquid reformate from separator 14 passes to ex traction zone 16 for separation of the aromatics from nonaromatic hydrocarbons. Zone 16 preferably is a solvent extraction zone in which countercurrent contact of the reformate with a selective solvent, such as diethylene glycol containing a minor amount of water, is effected to dissolve the aromatics and the extracted aromatics are thereafter stripped from the solvent. Alternatively, extraction zone 16 can employ a selective adsorbent such as silica gel instead of a solvent. The resulting extract,

3 which is removed through line 17, is a mixture of benzene and toluene which thereafter can be distilled to isolate the individual aromatics.

Raffinate which leaves the extraction zone via line 18 typically may amount to about 60% by volume of the virgin naphtha charged and have the following composition:

Comparison of this composition with that given hereinbefore for the charge shows that conversion of the cyclohexanes and dimethylcyclopentanes during the reforming step is high but that the conversion of methylcyclopentane is relatively low.

The rafiinate from line 18 passes to distillation zone 19 which is operated in a manner to segregate a heart cut which is rich in methylcyclopentane, preferably containing at least of this component. A light saturate fraction which boils (say) below 150 F. is removed through overhead line 20, the methylcyclopentane-rich fraction, which, for example, may boil through the range of 150-170 F., is taken as a sidestream through line 21, and a heavier saturate fraction boiling in the range of 170-220 F. is obtained as bottoms via line 22. Typical yields of these fractions based on the raffinate charged to distillation zone 19 are 30% of the low boiling saturates, 20% sidestream fraction containing about methylcyclopentane, and 50% bottoms fraction. The methylcyclopentane-rich fraction is recycled through line 13 for reforming in admixture with the virgin naphtha.

As previously stated the methylcyclopentane-rich fraction alternatively can be subjected separately to hydroforming conditions in either another reforming zone or in zone 12 utilizing a blocked-out operation. When this is done, milder hydroforming conditions generally should be used, as compared to the conditions for hydroforming the virgin naphtha, due to the greater tendency of methylcyclopentane to crack during reforming as compared to the other naphthenes in the virgin naphtha.

I claim:

1. Method of preparing benzene and toluene which comprises reforming a mixture of straight run naphtha boiling in the range of ISO-220 F. with hereinafter specitied recycle fraction in the presence of a platinum-containing reforming catalyst, said reforming being carried out in the presence of hydrogen at a pressure of 200-600 p.s.i.g., a molar ratio of hydrogen to hydrocarbon in the range of 2:1 to 5:1 and a temperature of 875975 F., separating gaseous components from the reformate, directly extracting the reformate to separate a benzenetoluene extract from saturated hydrocarbon raifinate containing unconverted methylcyclopentane, distilling the raffinate to separate a methylcyclopentane-rich fraction boiling in the range of -170 F. from lower and higher boiling hydrocarbons, and recycling all said methylcyclopentane-rich fraction as the said recycle fraction.

2. Method of preparing benzene and toluene which comprises reforming a straight run naphtha boiling in the range of 150-220" F. in the presence of a platinumcontaining reforming catalyst, said reforming being carried out in the presence of hydrogen at a pressure of 200-600 p.s.i.g., a molar ratio of hydrogen to hydrocarbon in the range of 2:1 to 5:1 and a temperature of 875-975 F., separating gaseous components from the reformate, directly extracting the reformate to separate a benzenetoluene extract from saturated hydrocarbon rafiinate containing unconverted methylcyclopentane, distilling the rafrinate to separate a methylcyclopentane-rich fraction boiling in the range of 150170 F. from lower and higher boiling hydrocarbons, and reforming all said methylcyclopentane-rich fraction in the presence of a platinum-containing catalyst under the above-specified reforming conditions to convert methylcyclopentane to benzene.

References Cited in the file of this patent UNITED STATES PATENTS 2,721,884 Ruedisulj Oct. 25, 1955 2,847,363 Nixon Aug. 12, 1958 2,853,437 Haensel Sept. 23, 1958 2,880,164 Viland Mar. 31, 1959 2,908,626 Poll Oct. 13, 1959 2,914,460 Kimberlin et al Nov. 24, 1959 2,915,455 Donaldson Dec. 1, 1959 2,933,445 Donnell et a1. Apr. 19, 1960 2,947,683 Hennig Aug. 2, 1960 2,968,607 Higley Jan. 17, 1961 

1. METHOD OF PREPARING BENZENE AND TOLUENE WHICH COMPRISES REFORMING A MIXTURE OF STRAIGHT RUN NAPHTHA BOILING IN THE RANGE OF 150-220*F. WITH HEREINAFTER SPECIFIED RECYCLE FRACTION IN THE PREESENCE OF A PLATINUM-CONTAINING REFORMING CATALYST, SAID REFORMING BEING CARRIED OUT IN THE PRESENCE OF HYDROGEN AT A PRESSURE OF 220-600 P.S.I.G., A MOLAR RATIO OF HYDROGEN TO HYDROCARBON IN THE RANGE OF 2:1 TO 5:1 AND A TEMPERATURE OF 875-975*F., SEPARATING GASEOUS COMPONENTS FROM THE REFORMATE, DIRECTLY EXTRACTING THE REFORMATE TO SEPARATE A BENZENETOLUENE EXTRACT FROM SATURATED HYDROCARBON RAFFINATE CONTAINING UNCONVERTED METHYLCYCLOPENTANE, DISTILLING THE RAFFINATE TO SEPARATE A METHYLCYCLOPENTANE-RICH FRACTION BOILING IN THE RANGE OF 150-170*F. FROM LOWER AND HIGHER BOILING HYDROCARBONS, AND RECYCLING ALL SAID METHYLCYCLOPENTANE-RICH FRACTIONS AS THE SAID RECYCLE FRACTION. 